In twin engine power boats having twin propellers, each driven by its own internal combustion engine, it is important, for proper maneuvering of the boat, to ensure that the two engines are in synchronism at all times. Further, if the engines are not synchronized, vibrations develop which are injurious to both the boat and the engines, and a highly unpleasant throbbing noise occurs.
In twin engine boats, there conventionally is provided a transversely spaced pair of throttle valve control levers, mounted pivotally relative to a throttle lever housing, each lever controlling the throttle valve for one of the engines. The levers are selectively advanced manually, relative to the housing, to cause the engines to operate at various speeds, ranging from idle or slow speed through various cruising speeds up to maximum or full speed. At all engine speed settings, it is necessary that the two throttle valve control levers be maintained in synchronous engine settings relative to each other, for proper operation of the boat.
When a boat is operating at a selected cruising speed, the throttle valve control levers are permitted to remain in their selected advance position or setting as the boat cruises. When it is necessary to slow the boat down, the levers are retracted to reduce engine speed. When the throttle levers again are advanced, to restore the boat to cruising speed, it is necessary to resynchronize the throttles, by appropriate manipulation of their levers, when the levers are back in cruising position.
It frequently is necessary to reduce the speed of a boat from cruising speed to slow or idle speed many times during the course of a day, particularly when cruising along populated stretches of water, such as in marinas, or through crowded waterways, passing docks or other boats, etc. It is not unusual, in the course of cruising or crowded waterways, to be required to slow the speed of a boat as many as three hundred times a day. Each time that occurs, it is necessary, when resuming cruising speed, to meticulously reset the throttle levers to resynchronize the throttles, to ensure that the operating speed of the engines is uniform and in synchronism. This is a frustrating and wearying experience, even for experienced pilots. It is a very difficult experience for inexperienced pilots.
So far as is presently known, no moderately priced, dependable, easily installed mechanical throttle synchronizer has been developed to permit the throttle valve control levers of a twin engine power boat, after slowing down the speed of the boat, to be quickly and accurately restored to a selected boat cruising speed location with concomitant accurate and automatic resynchronization of the engines at the selected boat cruising speed. Stop mechanisms for limiting the range of movement of throttle levers are old per se, as illustrated by the following patents: U.S. Pat. Nos. 1,427,969, 1,458,013, 1,479,108, 2,348,265, 2,613,547, 3,199,368 and 3,452,616. But they are not directed to the problem of engine resynchronization of twin engine power boats, nor do they even recognize that problem.